linux-kernel - Re: [PATCH] fs/dcache: prevent repeated locking

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Date:   Tue, 7 Dec 2021 13:25:18 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     cgel.zte@...il.com, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lv Ruyi <lv.ruyi@....com.cn>, Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] fs/dcache: prevent repeated locking

On Tue, Dec 07, 2021 at 01:17:41PM +0000, Matthew Wilcox wrote:
> On Tue, Dec 07, 2021 at 10:16:46AM +0000, cgel.zte@...il.com wrote:
> > From: Lv Ruyi <lv.ruyi@....com.cn>
> > 
> > Move the spin_lock above the restart to prevent to lock twice 
> > when the code goto restart.
> 
> This is madness.
> 
> void d_prune_aliases(struct inode *inode)
>         spin_lock(&inode->i_lock);
>                         if (likely(!dentry->d_lockref.count)) {
>                                 __dentry_kill(dentry);
>                                 goto restart;
> ...
> static void __dentry_kill(struct dentry *dentry)
>         if (dentry->d_inode)
>                 dentry_unlink_inode(dentry);
> ...
> static void dentry_unlink_inode(struct dentry * dentry)
>         spin_unlock(&inode->i_lock);
> 
> Did you even test this patch?

This same wrong patch has been sent several times before.  I think it's fair to
say that this code could use a comment, e.g.:

	/* i_lock was dropped */
	goto restart;

- Eric